1. Field of the Invention
The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus which can use a functional unit that can be detachably mounted in a main body of the image forming apparatus and that includes a nonvolatile memory capable of communicating with the main body of the image forming apparatus.
2. Description of the Related Art
FIG. 9 is a cross-sectional view illustrating the configuration of an electrophotographic printer, serving as an image forming apparatus.
In FIG. 9, an electrostatic latent image is formed on a photosensitive drum 1. A charging roller 2 uniformly charges the photosensitive drum 1. An optical unit 6 scans the photosensitive drum 1 with a laser beam 6. The laser beam 6 is emitted from the optical unit 5. A developing unit 3 develops the electrostatic latent image formed on the photosensitive drum 1 by the laser beam 6, using a toner.
A transfer roller 4 transfers the toner image formed on the photosensitive drum 1 onto a predetermined sheet. A fixing unit 7 fuses and fixes the toner on the sheet. Printing sheets are mounted in a standard cassette 8. A standard-cassette sheet feeding roller 9 picks up a sheet from the standard cassette 8.
There are also shown a manual sheet insertion tray 10, and a manually-inserted-sheet feeding roller 11. Discharging rollers 12 discharge the sheet to the outside of the printer. A registration sensor 13 performs registration of the leading edge of the sheet for printing by detecting the leading edge of the conveyed sheet. A discharged-sheet sensor 14 confirms that the sheet has normally been discharged through the fixing unit 7. A sensor 15 detects the presence/absence of sheets in the standard cassette 8. A sensor 16 detects the presence/absence of sheets for manual insertion. A process cartridge 17 includes the photosensitive drum 1, the charging roller 2 and the developing unit 3, and is detachable relative to the main body of the printer. The sheet after printing is discharged onto a discharged-sheet tray 18.
Each of these units operates according to an instruction from an engine control unit (to be described later). The engine control unit also performs printing processing by controlling the units based on instructions from a printer controller (to be described later).
The process cartridge 17 is usually used in order to facilitate maintenance of the printer. It has been proposed to provide a nonvolatile memory within the process cartridge 17, and write data relating to the state of use of the process cartridge 17 and other data in the nonvolatile memory, for example, in order to control the life of the photosensitive drum 1 included in the process cartridge 17.
FIG. 10 is a block diagram illustrating an example of control units of the printer.
In FIG. 10, a printer controller 101 performs communication with a host computer, develops received image data into information that can be printed by the printer, and exchanges signals with an engine control unit 102. The engine control unit 102 controls the respective units within the printer by means of serial communication.
A sheet-conveyance control unit 103 executes feeding and conveyance of the printing sheet from each sheet feeding unit (or sheet feeding tray) to the discharged-sheet tray 18, based on instructions from the engine control unit 102. An optical-system control unit 104 executes driving of a scanner motor for scanning the photosensitive drum 1 by the laser beam 6, and on/off control of the laser beam 6, based on instructions from the engine control unit 102. A high-voltage-system control unit 105 provides high-voltage outputs necessary for an electrophotographic process, such as charging, development, transfer and the like, based on instructions from the engine control unit 102.
A fixing-temperature control unit 106 performs temperature control of the fixing unit 7 based on an instruction from the engine control unit 102, detection of abnormality in the fixing unit 7, and the like, based on instructions from the engine control unit 102. A sheet-sensor input unit 107 transmits information from sheet sensors within the sheet feeding units (the cassette and the tray) and a sheet conveying path to the engine control unit 102. A jam detection unit 108 detects a failure during sheet conveyance. A failure detection unit 109 detects a failure within the printer. A process cartridge in which, as shown in FIG. 10, a nonvolatile memory 111 capable of exchanging data with the engine control unit 102 is mounted, and data can be read from and written into the engine control unit 102 has also been proposed as the process cartridge 17.
In the above-described configuration, the following approach may be considered as an approach for accessing the nonvolatile memory 111 from the printer controller 101.
The engine control unit 102 performs the processing of reading the entire contents of the nonvolatile memory 111 with a predetermined timing, and storing the read contents into a memory (not shown) within the engine control unit 102. When the engine control unit 102 is requested the contents of the nonvolatile memory 111 from the printer controller 101, the contents which have been read from the nonvolatile memory 111 and stored in the memory within the engine control unit 102 are transmitted to the printer controller 101.
FIG. 11 illustrates a protocol for such processing in the form of a timing chart.
A /SCLK signal is a clock signal for synchronism of serial communication output from the printer controller 101 to the engine control unit 102. A /SC signal is a command/status signal output/responded in synchronization with the clock signal for synchronism. A command is instruction information output from the printer controller 101 to the engine controller 102. A status is status information relating to the engine control unit 102 transmitted from the engine control unit 102 in response to the command from the printer controller 101.
Upon reception of a command 120 to request reading of memory contents A from the printer controller 101, the engine control unit 102 instantaneously transmits information relating to the memory contents A read in advance from the nonvolatile memory 111 and stored in the memory of the engine control unit 102, as status data 121.
However, since the above-described approach is specified such that the engine control unit 102 instantaneously responds to a request of reading/writing of the contents of the memory 111 from the printer controller 101, the engine control unit 102 must acquire in advance the entire contents of the nonvolatile memory 111 and store the acquired contents in the memory provided in the engine control unit 102.
Accordingly, the engine control unit 102 must have a surplus memory capacity covering the capacity of the nonvolatile memory 111. If information to be stored in the nonvolatile memory 111 increases, not only the memory capacity of the nonvolatile memory 111 but also the memory capacity of the engine control unit 102 must be increased, resulting in an increase in the cost of the apparatus.
Particularly if a cartridge mounting a nonvolatile memory whose capacity is larger than the capacity of the memory incorporated in the engine control unit 102 appears in the future, there is the possibility that the cartridge 17 cannot be normally utilized if the capacity of the memory of the engine control unit 102 cannot be increased.
It is an object of the present invention to provide an image forming apparatus in which a detachable unit mounting a memory is mountable in a main body of the apparatus, and in which the capacity of a memory mounted in the main body of the apparatus can be smaller than the capacity of the memory mounted in the detachable unit.
It is another object of the present invention to provide an image forming apparatus which provides a new protocol for accessing a nonvolatile memory from a printer controller.
According to one aspect, the present invention which achieves these objectives relates to an image forming apparatus mountable a detachable functional unit including storage means. The apparatus includes access-request provision means for providing a request of an access relating to reading or writing of data from or into the storage means, and access means for detecting the request of the access and for performing an access corresponding to the request of the access with respect to the storage means. The access means notifies the access-request provision means of completion of the access. Upon reception of the notification, the access-request provision means detects the completion of the access of the access means, and provides the access means with a request of transmission of a result of the access when the request of the access is reading of data from the storage means. The access means transmits the result of the access in response to the request of transmission of the result of the access.
According to another aspect, the present invention which achieves these objectives relates to a storage medium storing a control program for an image forming apparatus mountable a detachable functional unit including storage means. The control program includes an access-request provision program for providing a request of an access with respect to the storage means, and an access program for detecting the request of the access and for performing an access corresponding to the request of the access with respect to the storage means. The access-request provision program detects completion of the access of the access program, and provides the access program with a request of transmission of a result of the access when the request of the access is reading of data from the storage means. The access program transmits the result of the access in response to the request of transmission of the result of the access.
The foregoing and other objects, advantages and features of the present invention will become more apparent from the following description of the preferred embodiments taken in conjunction with the accompanying drawings.